The invention relates to a sealing and guiding packet for shock dampers. By means of such sealing and guiding packets, hydraulic shock dampers are sealed up on the one hand, and on the other hand these sealing and guiding packets serve to guide the piston rod in its oscillating movement. To achieve the sealing of the upper working space of the shock damper from the atmosphere, the sealing and guiding packet sealingly engages the interior wall of the shock damper tube on the one hand, while on the other hand it comprises a gasket which sealingly engages the surface of the piston rod which is in oscillating movement.
In the state of the art, numerous designs of such sealing and guiding packet are known. Thus, a sealing and guiding element is disclosed in DE 199 38 084, which has a guiding sleeve that is displaceable over a portion of the stroking movement of the piston rod and is joined to a spring element thrusting against a housing or an abutment body. The sealing element coming in contact with the piston rod is disposed for movement in common with the guiding sleeve. In this way, friction influences which act between the sealing element and the piston rod and lead to impairments of riding comfort are avoided. The friction between the sealing element and the piston rod can consequently lead to impairments of driving comfort, because, for example, the desired yielding motion of the vehicle's wheel, especially in small, shock-like stresses, due to sticking of the guiding sleeve or damping element on the piston rod is prevented or delayed (the so-called “stick-slip effect.” A prevented or delayed inward springing movement of the vehicle wheel results in the introduction of especially undamped and/or unsprung disturbing forces into the vehicle's frame. To avoid this so-called “stick-slip effect” and thus achieve an improvement of riding comfort, it is proposed in DE 199 38 084 A1 to make both the sealing element and the guiding sleeve movable. This solution is comparatively expensive because important components of the entire sealing and guiding packet have to be made able to move. It is furthermore disadvantageous that the movement of the guiding sleeve inevitably involves wear due to movement.
The invention is addressed to the problem of making available a scaling and guiding packet for shock absorbers, which minimizes or entirely avoids the negative effects of the stick-slip effect, so that traveling comfort is improved.
In the inventive sealing and guiding packet, an elastomer element envelops the cylindrical ring which is in sealing contact with the piston rod. The elastomer element is shaped in an especially advantageous manner, so that the packet is optimally supported resiliently in the axial direction. The radially extending flanges of the elastomer element, which support the ring on their end faces, provide this optimal resilient support. At the same time, the elastomer element has an additional, shorter flange which acts on the circumferential surface of the cylindrical ring and biases the ring against the piston rod. By this bias it is assured that a ring will always sealingly engage the surface of the piston rod.
The resilient support of the ring has the consequence that, in the case of small movements of the piston rod in which the ring still adheres to the piston rod, the elastomer element moves on account of its resilient properties. Thus no peak forces occur any longer due to the so-called stick-slip effect. If the movements of the piston rod become greater, the elastomer element can no longer yield and the ring separates from the piston rod. In this manner, the effects developed by the stick-slip effect, which are disadvantageous to riding comfort, are effectively minimized or, in the ideal case, entirely avoided.
To protect the ring against tipping and jamming and hold it in position, it is advantageous if protective disks are disposed between the end faces of the ring and the lips of the elastomer element supporting them. These supporting disks can consist, for example, of a steel material.
The biasing elements can be made in different ways pursuant to the invention. In a first embodiment of the invention, the sealing and guiding packet includes a substantially cylindrical base body which has a recess into which the elastomer element can be inserted. The recess in the base body of such dimensions in proportion to the radial position of the piston rod that when the elastomer element is inserted into the base body or when the sealing and guiding packet is inserted into the shock damper, the elastomer element becomes compressed in the radial direction, so that a radial bias of the ring against the piston rod is the result. The axial bias of the elastomer element is achieved by a cover which is mounted on the base body with axial compression of the elastomer element. The elastomer element is thus compressed in the axial direction, so that a bias of the elastomer element acts axially against the seal.
In a second embodiment of the invention, pressure channels are present in which a fluid under pressure is situated. Through these pressure channels a pressure is directed against the face of the elastomer element turned away from the shock absorber's interior, which counteracts the pressure from the working chamber of the shock absorber. In this way the elastomer element is relieved of pressure. The fluid that is under pressure, which for example can be the pressurized damping fluid of the shock damper, acts either directly on the elastomer element, or the effect of the pressure on the elastomer element is transferred indirectly to the elastomer element, by the interposition of one or more additional supporting elements. The internal pressure of the shock absorber, which otherwise would force the elastomer element together with the ring upwardly is thereby compensated. In the ideal case, a complete relief of pressure on the elastomer element is achieved through the pressure passages, so that the elastomer element rests in the sealing and guiding packet without having to absorb an axial pressure load. The axial and radial bias of the elastomer element is achieved in the second embodiment in the same way as in the first embodiment.
In the third embodiment of the invention the biasing of the elastomer element, again like the first embodiment of the invention, is achieved [through] a pressure passage, i.e., the radial and axial biasing of the elastomer element is brought about in this third embodiment of the invention in a way similar to the above-described first embodiment of the invention. Unlike the second embodiment, in the third embodiment of the invention a pressure passage is disposed only above the elastomer element (i.e., on the side facing away from the shock damper's interior), and it is connected with a gas chamber that is under pressure, so that a gas that is under pressure is active in the pressure passage. This gas under pressure can act directly or indirectly on the elastomer element. Thus the internal pressure of the damper, by which the ring or the elastomer element is thrust upwardly, is counteracted, so that the damper pressure is equalized and the elastomer element is relieved of pressure.
The third embodiment of the invention can be used to special advantage whenever the shock damper is a component of an air strut. In this case the pressure chamber of the air strut can be used for the purpose of preparing the gas under pressure for the relief of pressure.